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Fluorescent Lights Magically Activates iMac?

Posted by Cliff on from the weird-goings-on-here dept.

bats asks: "In my computer room at home, I have several machines -- and a fluorescent desk lamp. Among my various boxen is an iMac DV (slot loading) circa 1999. Its configured to go into power saving mode, but respond to wake-on-lan packets. The weird thing is this: If I flip on the fluorescent desk lamp, the sleeping iMac will suddenly wake up! This happens with 100% consistency. The desk lamp is plugged into a power strip and into the wall. The iMac is plugged into a UPS and then into the wall. The network switch for the room is near the desk lamp (1-2 feet) but the iMac is some distance away (8-10 feet). My question is: WTF?! How the heck does the iMac know when the light comes on? It seems like it must be some power spike in the AC or noise on the network interface. However, the power strip and the UPS should block an AC spike and the chance of electrical noise in the cat-5 looking like a wake-on-lan packet seem more than miniscule. So again I ask you, dear AskSlashdot reader, WTF?! I await conspiracy theories, pseudo-science, wild rantings, and hopefully, the right answer."

3 of 108 comments (clear)

  1. logical process... by invictus · · Score: 5, Insightful

    one way to go about figuring it out, i would think, would be to remove the mac from the lan, turn on the lamp... does it wake up? if it does you can rule out WOL. If it doesn't, then it seems to be something on the network. Is the hub/switch plugged into the same surge protector as well as being perhaps too close? just step through the problem.

    --
    --Ks9
  2. EMI by Anonymous Coward · · Score: 2, Insightful

    My cordless-phone (900Mhz) base is about 2 feet above my DSL bridge and hub. Any time there is activity on the ethernet/DSL and I'm on the phone, I can hear it as noise. On certain channels, the noise is more prevailant. Which means either the channel's frequency or one of its harmonics is near the frequency of the ethernet/DSL or one of its harmonics and the power is significant enough to be picked up by the phone. I would guess that a lot of power is needed to first "start" the flourecent lamp. The big "spike" causes enough EMI that your ethernet cable "picks up". The ethernet cable is then acting like an antennea. The wake-on-lan must just detect ANY activity on the ethernet, not a valid packet. Anyway, that's my guess.

  3. mouse + light by daniel2000 · · Score: 5, Insightful

    if you have a mouse anywhere near the light and then some light could be getting into the mouse makeing it think it has moved.

    Try the experiment with the mouse covered up with a rug and switching the light on.

    I had an experiance where at certain times of the day the mouse cursor would go a bit funny. took a while to work out it was when the sun peeped throught the window at just the right angle...